Field of the Invention and Related Art
This invention relates to a method of manufacturing a diffractive optical element.
A diffractive optical element is an optical element that uses a diffraction phenomenon of light, and it can be provided by a diffraction grating of various shapes and sizes. As an example, Japanese Laid-Open Patent Application, Laid-Open No. 258510/1994 shows a diffractive optical element with a diffraction grating having a step-like sectional shape. This diffractive optical element is formed by alternately accumulating, upon a substrate, layers of two materials having different reaction characteristics, with respect to an etching gas, while their film thicknesses are precisely controlled. After this, a patterning operation and an etching operation are performed to the alternate layers of the two materials on the basis of photolithography, by which a diffraction grating of step-like shape is produced.
Where a diffraction grating having a step-like sectional shape is produced in accordance with the method disclosed in Japanese Laid-Open Patent Application, Laid-Open No. 258510/1994 mentioned above, if the patterning is performed three times in a superimposed fashion, an alignment error may occur between a step and a side wall facing it. If this occurs, the side wall may have a slope extending from the bottom of the step. That is, in the step-like structure, the side wall does not extend perpendicularly to the bottom.
Further, in accordance with the method of forming a diffraction grating as disclosed in Japanese Laid-Open Patent Application, Laid-Open No. 258510/1994 mentioned above, a resist is applied to a surface having a surface step as defined by the etching process, and then the subsequent patterning operation is performed. This causes the side wall of the patterned resist, particularly, the resist side wall of a lower step (smaller level difference), is easily affected by a wall on the opposite side, during the exposure operation, such that there occurs a tilt of the resist side wall relative to the bottom. As a result, the step-like shape to be defined by the subsequent etching process is formed with a similar tilt like the resist tile shape.
It is an object of the present invention to provide a method of manufacturing a micro-structure having an accurate step-like sectional shape.
It is another object of the present invention to provide a diffractive optical element with a diffraction grating having such a structure.
In accordance with a first aspect of the present invention, there is provided a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: etching a first region of a substrate, corresponding to a lowest step of the step-like element, with an appropriate depth, whereby a surface of the lowest step of the step-like element is defined; and etching, subsequently, a second region of the substrate, corresponding to another step of the step-like element, with an appropriate depth, whereby a surface of that step of the step-like element is defined.
In accordance with a second aspect of the present invention, there is provided,a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: forming, on a substrate, a film having a thickness corresponding to the height of the step-like element; etching a first region of the film on the substrate, corresponding to a lowest step of the step-like element, with an appropriate depth, whereby a surface of the lowest step of the step-like element is defined; and etching, subsequently, a second region of the film on the substrate, corresponding to another step of the step-like element, with an appropriate depth, whereby a surface of that step of the step-like element is defined.
In accordance with a third aspect of the present invention, there is provided a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: forming, on a substrate, a film. having a thickness corresponding to the height of the step-like element; etching a first region of the film on the substrate, corresponding to a lowest step of the step-like element, with an appropriate depth, whereby a surface of the lowest step of the step-like element is defined; and etching, subsequently, a second region of the film on the substrate, corresponding to another step of the step-like element, with an appropriate depth, whereby a surface of that step of the step-like element is defined, wherein the film includes a multilayered film comprising alternate layers of two materials having different etching rates, and wherein each layer of one of the two materials having a higher etching rate serves as a main portion of the step-like element, while each layer of the other material having a lower etching rate serves as a stopper when the or each layer of the material of the higher etching rate is etched.
In accordance with a fourth aspect of the present invention, there is provided a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: forming, on a substrate, a film having a thickness corresponding to the height of the step-like element; etching a first region of the film on the substrate, corresponding to a lowest step of the step-like element, with an appropriate depth, whereby a surface of the lowest step of the step-like element is defined; and etching, subsequently, a second region of the film on the substrate, corresponding to another step of the step-like element, with an appropriate depth, whereby a surface of that step of the step-like element is defined; wherein the film includes a multilayered film comprising alternate layers of two materials having different etching rates; wherein each layer of one of the two materials having a higher etching rate serves as a main portion of the step-like element while each layer of the other material having a lower etching rate serves as a first stopper layer when the or each layer of the material of the higher etching rate is etched; and wherein the film further includes a second stopper layer of a material having an etching rate lower than those of the two materials and being provided on a side of the multilayered film facing the substrate, the second stopper layer serving as a stopper when the two materials are etched.
In accordance with a fifth aspect of the present invention, there is provided a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: etching a region of a substrate with an appropriate depth; and etching, subsequently, a surface defined by said etching and corresponding to a side wall of the step-like element.
In accordance with a sixth aspect of the present invention, there is provided a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: etching a xe2x80x2 region of a substrate to provide a surface of a step of the step-like element; and etching, subsequently, a surface defined by said etching and corresponding to a side wall of the step-like element, to correct an angle of the surface corresponding to the side wall.
In accordance with a seventh aspect of the present invention, there is provided a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: forming, on a substrate, a film having a thickness corresponding to the height of the step-like element; etching a region of the film of the substrate with an appropriate depth; and etching, subsequently, a surface defined by said etching and corresponding to a side wall of the step-like element, to correct an angle of the surface corresponding to the side wall; wherein the film includes a multilayered film comprising alternate layers of two materials having different etching rates; wherein each layer of one of the two materials having a higher etching rate serves as a main portion of the step-like element while each layer of the other material having a lower etching rate serves as a stopper when each layer of the material of the higher etching rate is etched; and wherein each layer of the one material having the higher etching rage is etched so that the or each layer of the other material having the lower etching rate is exposed, and thereafter the etching step for the correction of the angle of the surface corresponding to the side wall is performed while each layer of the material of the lower etching late is kept exposed.
In accordance with an eighth aspect of the present invention, there is provided a method of manufacturing a micro-structure having a plurality of step-like elements, said method comprising: forming, on a substrate, a film having a thickness corresponding to the height of the step-like element; and etching a region of the film of the substrate with an appropriate depth; wherein the film includes a multilayered film comprising alternate layers of two materials having different etching rates; wherein each layer of one of the two materials having a higher etching rate serves as a main portion of the step-like element while each layer of the other material having a lower etching rate serves as a stopper when each layer of the material of the higher etching rate is etched; and wherein each layer of the one material having the higher etching rage is etched until each layer of the other material having the lower etching rate is exposed, and thereafter a resist pattern is formed on the substrate where the lower etching rate material layer is exposed, wherein each layer of the lower etching rate material is etched by use of the resist pattern and, thereafter, each layer of the higher etching rate material below it is etched.
In a ninth aspect of the present invention, there is provided a method of manufacturing a diffractive optical element, including a process for forming a diffraction grating in accordance with the method corresponding to any one of the first to eights aspects of the present invention.
In a tenth aspect of the present invention, there is provided a method of manufacturing a diffractive optical element, including a process for forming a mold for a diffraction grating in accordance with the method corresponding to any one of the first to eights aspects of the invention, and for forming the diffraction grating, for the diffractive optical element, by using the mold.
In an eleventh aspect of the present invention, there is provided a method of manufacturing an optical system having a diffractive optical element, including a process for providing the diffractive optical element in accordance with the method corresponding to any one of the first to eights aspects of the invention.
In a twelfth aspect of the present invention, there is provided a method of manufacturing an optical system having a diffractive optical element, including a process for forming a mold for a diffraction grating in accordance with the method corresponding to any one of the first to eights aspects of the invention, and for providing the diffractive optical element by using the mold.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.